This project is designed to test a central hypothesis that oral sub-mucosal injection of SHIV virus-like particles (VLPs) genetically engineered with CD40 ligand (CD40L/SHIV-VLPs) will induce strong and long lasting systemic and mucosal immune responses against HIV infection through dendritic cell (DC) activation at the mucosal tissues and local draining lymph nodes (LN) (cervical LN). CD40L is an antigen presentation cell (APC) maturation signal. The major focus of our proposed project is to characterize oral mucosal immune responses elicited by chimeric CD40L/SHIV VLPs, to investigate the mechanism of chimeric CD40L/SHIV VLPs induced mucosal immune responses in the mouse and monkey models, and to test the protective efficacy of this vaccine strategy by mucosal SHIVSF162P4 or SIVmac239 challenge in rhesus macaques. We propose four specific aims: 1). To determine whether mCD40L/SHIV VLP oral sub-mucosal immunization can bind to sub-mucosal dendritic cell subsets to elicit strong mucosal HIV specific immune responses in mice;2). To determine the best immunization strategy of hCD40L/SHIV VLPs to induce strong mucosal and systemic humoral and cellular immune responses and to protect virus challenge in non-human primates;3). To decipher the mechanism of hCD40L/SHIV VLP oral sub-mucosal vaccination in inducing strong mucosal immune responses in non-human primates;and 4). To determine the protective effect of hCD40L/SHIV VLP mucosal vaccination from pathological SIVmac239 or SHIVSF162P4 challenge in a non-human primate model. This study is a critical step towards clinical trials and applications with new vaccine strategies to prevent HIV infection.